In a multipoint content sharing system, a sender delivers content to multiple receivers. In real-time content sharing applications, a quick response to newly-joined attendees enhances user experience. An instantaneous decoding refresh (IDR) frame in the H.264 standard is used as a response frame. This is because that the IDR frame applies only intra-frame prediction and does not depend on any previously decoded frame during its decoding.
In response to a request from any receiver in a multipoint sharing session, the sender needs to send out an IDR frame to all receivers. When a new receiver joins, an IDR frame is needed since there is no previously decoded frame to be referred to at the newly-joined receiver.
On the other hand, it is observed that the compression efficiency of frames applying only intra-prediction can be low in screen content coding using H.264. Given the common case that the resolution of screen content sharing is relatively large, the data size of an IDR frame will be very large. Thus, when an IDR frame is to be sent, the data burst can deteriorate the uplink channel.
These factors contribute to the disadvantages of the traditional system of screen content sharing using H.264. A request from any receiver will invoke an IDR frame at the sender, but sending the IDR frame may result in worsening the video experience at all receivers. Controlling the number of IDR frames or data size of each IDR frame may alleviate the problem but at the expense of keeping some receivers waiting, or of lower video quality at all receivers, respectively.
A sophisticated system should be able to balance among the server capacity, network conditions, requests from individual receivers and the user experience of all users in the system.